Fuel injectors are known which comprise an inlet connected to a fuel supply pump; a nozzle communicating with the inlet to inject fuel into the engine; and a shutter pin, which is moved axially, to open and close the nozzle, by the opposite axial thrusts exerted by the pressure of the injected fuel, on one side, and by a positioning spring and a control rod, on the other.
The control rod is located along the axis of the pin, on the opposite side to the nozzle, is activated by an electromagnetic metering valve forming part of the injector, and is connected to the pin with the axial interposition of a cylindrical spacer body.
The spacer body is defined by two opposite flat surfaces crosswise to the axis and resting on the flat ends of the control rod and pin respectively, and is of an axial height calibrated according to given classes, and which is selected as a function of the desired maximum lift or axial stroke of the pin.
Known injectors of the above type are not always satisfactory, owing to the resultant of the contact pressures between the spacer body and the pin being applied at a normally indefinite point, and normally generating on the pin undesired transverse forces crosswise to the axis.
The pressures exerted by the spacer body on the pin, in fact, are not always distributed evenly over the mutually contacting surfaces, mainly on account of inevitable flatness and roughness tolerances, so that the resultant of the pressures sometimes generates on the pin rotation torques about a direction perpendicular to the pin axis.
Said transverse forces are sometimes also generated by the mutually contacting surfaces of the spacer body and pin not being perfectly perpendicular to the pin axis.
Such transverse forces produce relatively severe friction forces along the seat in which the pin slides, thus resulting in an anomalous increase in wear and, therefore, in the radial clearance between the pin and seat. This in turn results in an undesired increase in leakage of the unused fuel, which flows out of the injector through a recirculating outlet.
The increase in leakage and, therefore, in the amount of fuel recirculated may result in the pump being unable to supply the injectors in all engine operating conditions.